A measuring method that uses a sensing device equipped with a quartz sensor using a quartz resonator for sensing a substance in minute quantities such as an environmental pollutant e.g. dioxine or the like, or a disease marker for the hepatitis C virus, a C-reactive protein (CRP), or the like has been widely known.
To be more specific, the measurement method is conducted in such a manner that an adsorbing layer is formed in advance on an excitation electrode on one surface side of the quartz resonator, and the presence/absence of the object to be measured or the concentration thereof in a sample solution is measured by applying a property that when the object is adsorbed, the resonance frequency of the quartz piece varies according to the mass of the adsorbed substance. In Patent Document 1, there is a description that for the purpose that the quartz resonator equipped in the quartz sensor used in this measurement method be oscillated in a stable fashion in an immuno-latex solution, it is desirable to have a structure in which only one surface of the quartz resonator comes in contact with a measurement medium.
Such a quartz sensor is usually called a Langevin type quartz resonator. Though not described in Patent Document 1, the fundamental structure of the Langevin type quartz resonator generally has a composition shown in FIG. 10. 10 in the drawing is a round quartz piece, and foil-shaped electrodes 11 and 12 are respectively formed at the center of both surfaces. Supporting line members 13 and 14 to take out an electric signal outside, lead wires of, for instance about 0.5 mm in diameter are connected to these electrodes 11 and 12. A base 16 having a recess 15 is placed on the other surface side of the quartz piece 10. The quartz piece 10 and the base 16 are adhered firmly by an adhesive 17, thereby forming an airtight space enclosed by the quartz piece 10 and the recess 15.
In recent years, further control of toxic substances which have a large effect on an environment such as the above-described dioxin or the like that has been demanded from the viewpoint of environmental protection, and attempts to achieve measurement in the ppt level have been widely conducted. In a quartz resonator, the resonance frequency of the quartz resonator increases as the thickness of the quartz piece decreases. From the Sauerbrey equation, the greater the frequency generated by the quartz resonator, the more the amount of deviation in frequency in regard to the amount of change in mass of the object. In other words, when the quartz piece becomes thinner and thinner, the measurement sensitivity of the quartz sensor increases, so that the measurement of a substance in minute quantities becomes possible. Therefore, reduction in the thickness of the quartz piece is required.
The technology to reduce the layer thickness of a quartz piece has progressed at present, and it has become possible to manufacture a quartz piece with a thickness of several to several tens of μm. As for a method of manufacturing a quartz sensor as shown in FIG. 10, a method in which a quartz resonator is sandwiched with, for instance, two plastic cases having a specific shape in a manner that an airtight space is formed between one surface of the quartz resonator and the plastics, so that the quartz resonator is fixed in the plastic cases by welding the plastic cases together by ultrasonic waves has been attempted. When such a method is used, however, the thin layered quartz piece is in danger of being damaged by the vibration due to the ultrasonic waves. It is also conceivable to adopt injection molding, but injection molding has the disadvantage of complicating the manufacturing process.
In Patent Document 2, there is a description of a structure prepared in such that a rectangular notch a little smaller than the quartz resonator is formed at the center of one side of a square flexible substrate, the quartz resonator is attached to the flexible substrate so that the quartz resonator is caught in the notch, and the flexible substrate, a high polymer elastic sheet, and a holding substrate are united by screwing them together. When taking this structure, it is possible to manufacture a quartz sensor without application of ultrasonic waves as described in the above method of manufacturing.
However, it is understood from the exploded perspective view of the quartz sensor in Patent Document 2 that it is structured in a manner that the periphery of the quartz resonator is sandwiched between the high polymer elastic sheet and the flexible substrate, and a strong force is applied on the periphery of the quartz resonator when the screw is fastened to ensure the airtightness. Accordingly, the possibility of damaged during the manufacturing process is much larger when the thickness of the quartz resonator is reduced.
In addition, though the quartz sensor functions as the detector in a sensing device by being connected to a measurement device main unit, which performs signal processings, when the quartz sensor is connected to the measurement device main unit, a special attachment is required in the method in Patent Documents 1 and 2. When measuring, for instance, 8 samples which are different in dilution ratio, are prepared from the same sample to be measured, and measurement for each sample is performed so as to increase the measurement accuracy. At this time, there is a disadvantage that the measurement work is troublesome because the wiring for the respective samples spread over a work bench which is used at the time of the measurement.
Patent Document 1: Japanese Patent Application Laid-open No. 2001-83154 (paragraph 0009, column 0019 and FIG. 1)
Patent Document 2: Japanese Patent Application Laid-open No. Hei 11-183479 (paragraph 0024, FIG. 2 and FIG. 9)